The special bags stayed dry inside when we gave each a brief dunking in water. They also kept out sand sprinkled along their seals. But the Hefty bag also passed both tests.

All the bags allowed us to control key functions of the devices. Screens could be swiped and pressed, for example, and volume and brightness controls could be adjusted.

We could even shoot photos, though the images were cloudy, especially when shot through the thicker bags. The bags’ shiny plastic also increased glare, so you may want to use them in the shade.

The tighter the bag, the easier the device was to use. The DryCase bags have a unique vacuum-sealing feature plus a headphone jack that’s protected against sand and water.

It took a few tries to eliminate wrinkling, but eventually we were able to seal the DryCase using the bulb-shaped hand pump that’s included. But you should be able to create a passable vacuum seal with many other bags by closing the seal all but the last half-inch or so, then pushing the air out before closing it completely.

Bottom line. We recommend that you bag your gear for the beach or any other place where handhelds might be ruined, say at a pool or on a camping trip. Any zipper or slider bag will probably provide passable protection, and the price is certainly right. Even a special bag will probably be less expensive than such alternatives as a special, supposedly weatherproof case, which also permanently adds weight and bulk.

Buy a few bags in different sizes to see which ones fit your gadgets the best. Consider replacing them periodically, particularly if sand has scratched the surface and affected how clearly you can see the screen and use its controls. Place devices in the bags before you leave home, and try not to remove them until you’re back home and have brushed sand and water off.

To take decent photos on the beach, though, you’ll need to unseal and remove your phone or camera. If that worries you, you can buy one of the heavy-duty cases or a new rugged device that's designed to be weatherproof. The latter includes the recommended Samsung Rugby Smart (for AT&T) and some recommended cameras (available to subscribers).

DryCase and DryCase Tablet

During testing, users found the touch screen to be responsive through the plastic.

These bags use a vacuum seal to keep water and sand from reaching your device: You insert your device and line up the two tabs to lock the bags. You then use the included bulb to pump out air. The DryCase ($29 for smaller handheld devices, $38 for tablets)also comes with a built-in headphone jack, an armband, and a lanyard.

Users found the bags a little hard to open, and it was a bit of a challenge to insert and remove devices. They needed a few tries to pump out air without leaving air bubbles and pockets, which affected the screen’s readability.

While relatively thick, the bags are is very clear. Users found touch screens to be responsive through the plastic. You can use your phone or other device while it’s in the bag, but phone calls sounded a little muffled, and pictures taken from within the bag weren’t as clear as usual. The bags also created some glare on screens.

Because of the vacuum seal, the bags had no problem in our water-immersion tests. While sand wiped away easily, it did stick inside the lock tabs and in the exposed headphone jack.

TrendyDigital WaterGuard Waterproof Case

The TrendyDigital WaterGuard Waterproof Case ($16) has a double zipper lock and two snaps to keep water and sand out, and it comes with an attached lanyard. It will fit a small to midsized handheld device.

The TrendyDigital bag is simple to open; you slip in your device and close the zips. You need to fold the top of the bag tightly to close the snaps, though, which is challenging. The TrendyDigital is slightly large for common smart phones and small e-book readers, but smaller tablets fit well. Devices don’t move around much inside the bag because the texture of the plastic holds them in place.

This bag is made from relatively thin plastic, so touch screens were responsive through the bag. Phone calls were slightly muffled, though. Due to the finish of the plastic, pictures taken by devices inside the bag were blurred out. And we saw a fair amount of glare on the screen during our readability tests, enough to make reading difficult. Because this bag did not have a snug fit, bubbles and air pockets also detracted from readability.

The double seals ensured no problems with our water-immersion tests. Sand wiped away easily but did stick inside the snaps and folds.

Seattle Sports Dry Doc Waterproof e-Tablet Case

Touch screens were responsive, though at times swiping pages was difficult.

The Seattle Sports Dry Doc Waterproof e-Tablet Case ($16) is a heavy-duty clear plastic presslock bag that can fit larger tablets, such as the Apple iPad. The single seal made inserting the devices easy.

Smaller handheld devices tended to move around inside the bag, so controls on the sides of the device were harder to activate. The thin plastic handle did not seem sturdy.

The Dry Doc uses a thin plastic, so touch screens were responsive, though at times swiping pages was difficult. Pictures taken with devices when they were in the bag lacked clarity compared with pictures taken outside of the bag.

A fair amount of glare was apparent on the screen during our readability tests, enough to make reading difficult. Because this bag did not have a snug fit, bubbles, air pockets, and wrinkles also detracted from readability.

There were no problems in our water immersion tests. The sand wiped away easily; none was left on the bag after our test.

Lavod LMB-011 Waterproof Bag

When the hard plastic became crinkly, at times it was difficult to read the display.

The Lavod LMB-011 Waterproof Bag ($19) uses three lock tabs to seal the device and protect it from water and sand. It comes with a detachable carrying strap and will fit larger tablets, such as the Apple iPad. Three locks seal the bag, making it fairly easy to close.

The stiffer plastic used in the bag made it less sticky than others, so the enclosed devices “floated” around inside. That made switches and buttons on the sides of the devices harder to activate.

Users also noted that the hard plastic became crinkly as they used enclosed devices, which at times made it difficult to read the display. Users did not see any effect on the responsiveness of the touch screen. Pictures taken while the devices were in the bag lacked clarity.

A fair amount of glare appeared on the screen during our readability tests, enough to make reading difficult. Users noted that the clear plastic bag was more reflective than others, further hampering display readability. Bubbles, air pockets, and wrinkles also detracted from readability.

The bag did well in our water-immersion tests. Sand wiped away easily, but it did stick inside the lock tabs.

Hefty Slider Bag, gallon size

There were no problems in our water-immersion tests, and sand wiped away easily.

The widely available gallon-size Hefty Slider Bag (about $4 for box of 30)uses a zipper to seal. The size we tested fits larger tablets, such as the Apple iPad. Hefty Slider Bags use one zipper, so it’s easy to insert a device.

The bag’s thin plastic made it less sticky, so enclosed devices (regardless of size) “floated” inside, making side controls harder to activate. Users did not see any effect on touch screens while performing basic tasks on devices in the bag. Pictures taken while the devices were in the bag lacked clarity.

Glare seen on the screen during our readability tests made reading difficult. Users also noted that the thinner plastic became crinkly as they used the enclosed devices, which at times made it difficult to read the display. Bubbles and air pockets also detracted from readability.

There were no problems in our water-immersion tests. The sand wiped away easily, but it did stick inside the zippered tab.